The present invention relates to a method for increasing the corrosion resistance of aluminum base alloys, which are particularly useful in primary cells of the "dry" type. The alloys are utilized as the anode material in said primary cells, said anode material also serving as the container for the cell. The alloys may also be utilized as anode material in applications which require resistance to corrosion, such as water heaters.
Zinc is extensively employed as anode material in the construction of dry primary cells, for example, in common flashlight batteries. Numerous proposals have been made to substitute aluminum or aluminum alloys for zinc as the anode material in dry cells in order to utilize the numerous advantageous properties of the aluminum or aluminum alloys. Aluminum and aluminum alloys are generally less expensive than zinc. As zinc becomes more and more scarce, this price differential will increase. Aluminum and aluminum alloys also enjoy a greater ease of fabrication to thin gages and particularly to formed dry cell battery cases.
Dry cell batteries containing aluminum, aluminum-zinc alloys or other aluminum base alloys as the anode material have, however, suffered from numerous significant disadvantages. Such cells generally require the placement of a semi-permeable membrane within the battery container to prevent the evolution of large volumes of hydrogen gas resulting from the aluminum-electrolyte reaction which takes place within the dry cell battery. Dry cell battery containers which have been manufactured from standard commercial aluminum alloys such as Aluminum Association Alloy 1100 are subject to unacceptable hydrogen gas evolution when used. Such hydrogen evolution causes the battery containers to either swell or, in extreme circumstances, to burst. Either condition is not acceptable to the ultimate consumer, since a swollen battery usually cannot be removed from a device into which it has originally been inserted and a battery which has burst may subject the consumer to dangerous corrosive chemicals.
As mentioned above, this evolution of hydrogen gas has presented a problem which the prior art has attempted to solve through the use of semi-permeable membrane within the battery case which retains the electrolyte material away from the aluminum of the anode casing. Such a solution has not been successful with the typical commercial aluminum alloys. Composite alloys which have been utilized to overcome the gas evolution disadvantage have not been entirely satisfactory and are also quite expensive.
The evolution of hydrogen gas from the former aluminum alloys has been the result of localized attack of said alloys. This attack, generally caused by the electrolyte utilized in the cell, is a classic example of aluminum alloy corrosion. Therefore, an aluminum alloy which can reduce the residence of hydrogen gas evolution can also be more resistant to corrosion than aluminum alloys formerly used. This resistance to corrosion can be useful in other applications such as anodes for water heaters and other operations which require resistance to corrosion.
It is, therefore, a primary object of the present invention to provide a method of increasing the corrosion resistance of aluminum base alloys.
It is a further object of the present invention to provide a method as above which enables improved aluminum base alloys to be useful as the anode container material for primary electric cells of the dry type.
It is a further object of the present invention to provide a method as above which enables improved aluminum base alloys to reduce the incidence of hydrogen gas evolution within primary cells as described above.
Further objects and advantages of the present invention will appear from a consideration of the following discussion.